The present invention relates to a honeycomb structure used as a filter, a catalyst carrier, or the like and a manufacturing method thereof.
A honeycomb structure is widely used as a filter, a catalyst carrier, or the like, and in particular, as a catalyst carrier, a filter, or the like, for purifying or treating exhaust gas from an internal combustion engine such as a gasoline engine or a diesel engine or a combustion apparatus.
As one of the methods for manufacturing a honeycomb structure used for such a purpose, there has been known a method for manufacturing a honeycomb structure having a coating member covering the outer periphery thereof by machining a peripheral portion of a honeycomb substrate having a plurality of-cells separated by ceramic porous partition walls to give a predetermined shape, applying slurry for forming a coating member on a face exposed to the outer periphery of the partition walls positioned in the outermost periphery, and drying the slurry.
A honeycomb shaped substrate as described above can generally be obtained by drying and/or firing a honeycomb-shaped formed body obtained by extrusion forming using clay made of predetermined raw materials. Since deformation is prone to be caused in the drying and firing steps, in the case of using the honeycomb substrate for a honeycomb structure requiring high shape precision to some degree, the peripheral portion is machined into a predetermined shape by grinding, or the like after drying or firing, and a surface of the partition walls exposed in the outer periphery by the machining is covered with a coating member, thereby manufacturing a honeycomb structure satisfying the required shape precision.
Such a honeycomb structure having a coating member covering the outer periphery has conventionally been manufactured by preparing slurry for forming a coating member containing an aggregate particle of a powder of potsherd or the like as the main component, applying the slurry on a face exposed to the outer periphery of the partition walls positioned in the outermost periphery of the honeycomb substrate subjected to machining to give a predetermined shape, leaving the honeycomb substrate with slurry in room temperature in the ambient air for natural drying, and subjecting the honeycomb to heat-drying as necessary (e.g., Japanese Patent No. 2613729).
The slurry for forming a coating member is not subjected to compulsory drying such as heat-drying from the beginning but dried naturally to some extent in the above conventional manufacture method because cracks are easily caused in the coating member if the slurry is dried and shrinks suddenly by compulsory drying from the beginning.
However, when the slurry for forming a coating member applied in such a manner is naturally dried, it requires long drying time and, and thereby time for manufacturing a honeycomb structure is increased as a whole. In the case of mass production, a large space for storing a large number of honeycomb structures is required upon drying.